For detecting the presence or absence of a target (for example, a vehicle or a person) in a wide angle range, a measurement technique using plural radar apparatuses (hereinafter, referred to as “sector radars”) has been proposed. For example, Patent Literature 1 discloses a radar system that suppresses interference between sector radars by using complementary codes as transmission codes in plural (for example, two) sector radars.
Two radar systems P and Q disclosed in Patent Literature 1 perform transmission and reception by carrier waves of the same frequency band using P1 and P2 in the radar system P and using Q1 and Q2 in the radar system Q as coded pulses of complete complementary sequences that are different from each other.
When the own radar system receives plural coded pulses transmitted by the own radar system, the own radar system outputs plural autocorrelation function signals RP1P1(τ) and RP2P2(τ) or RQ1Q1(τ) and RQ2Q2(τ) corresponding to the plural coded pulses P1 and P2 or Q1 and Q2. On the other hand, when the own radar system receives plural coded pulses transmitted by the other radar system, the own radar system outputs plural cross-correlation function signals RQ1P1(τ) and RQ2P2(τ) or RP1Q1(τ) and RP2Q2 (τ) corresponding to the plural coded pulses transmitted by the other radar system.
From a characteristic of the complete complementary sequences, the sum of the plural outputs of the autocorrelation functional signals (RP1P1(τ)+RP2P2(τ) or RQ1Q1(τ)+RQ2Q2(τ)) becomes zero when τ is not zero, and the sum of the plural outputs of the cross-correlation functional signals (RQ1P1(τ)+RQ2P2(τ) or RP1Q1(τ)+RP2Q2(τ)) becomes zero regardless of the value of τ.
Accordingly, with respect to the plural coded pulses (P1 and P2 or Q1 and Q2) transmitted by the own radar system, a reception side calculates plural autocorrelation function signals corresponding to the respective pulses, to thereby make it possible to obtain a compressed pulse in which a side lobe is not present, and even though the reception side receives the plural coded pulses transmitted by the other radar system, it is possible to make a signal component of the other radar system be zero in the process of calculating the sum of the autocorrelation function signals. Thus, even though the radar systems use the same frequency band in adjacent frequency bands, it is possible to mutually suppress interference.